The present invention relates to a cushion body having a steel spring assembly embedded therein, and a method of forming the same. More particularly, the invention is directed to such cushion body for use in an automotive seat, which employs a continuous coil-spring assembly comprising coil spring portions and linear connection parts connecting them integrally together.
2. Description of Prior Art
Coil-spring assembly of a unitary or continuous type, typically, includes an entangled spring assembly as shown in FIG. 1a, and a non-entangled, sequential coil-spring assembly as shown in FIG. 1b.
This sort of spring assembly is usually employed in forming a cushion body for automotive seat. Namely, the spring assembly is integrally embedded in a polyurethane cushion member (which will be referred to as a "urethane member"). FIGS. 2 to 4 illustrates examples of how the spring assembly is embedded in that member.
Those spring assemblies are formed by subjecting a straight spring material (a steel wire material), of approx. 2.0 .phi. in wire diameter, into a machining work process. Their given outer configurations are set due to their respective self-recovery properties, depending upon such conditions as their wire diameters, high-tensile strengths, and upon whether they are easy or hard to be worked by the machining process. This is found to be an obstacle limiting free design applicability in the case where the spring assemblies are used in the automotive seat, because of their non-flexibility for various formations in various dimensions.
Such continuous series of coil springs, which form a row of springs in a line, are normally subject to a settling or setting process, by repeating several strokes of applying a given load to the springs, so as to eliminate an initial changeable setting thereof. By such method, an initial height of springs (e.g. 150 mm) is settled down to a low, unchangeable height (e.g. 120 mm). However, a resulting spring produced by this setting process is unchageable in formation and thus can not be reduced in height. For this reason, the above-noted problem, namely, the dimensional limitations and limited desingn applicability, has remained yet to be solved.
This problem in particularly notable when such spring assembly is applied in an automotive bucket seat whose both sides are formed curved upward to project higher, each having stepped part. In this case, the urthane member has been formed thick at the corresponding area. Further, in the case of such rear-seat seat cushion having a tunnel area formed in its bottom, there has been no other way but to embed in the cushion member thereof a specially formed coil-spring assembly having a lower spring area.
Additionally, when the continuous coil-spring assembly is set in the molding for foaming together with the urethane member, it is difficult to dispose the assembly in a uniform way, although not requiring a frame wire member, particularly, it is difficult to set a proper height of the spring in order to leave an even thickness of urethane member above the spring.